1. Technical Field
The present invention relates in general to magnetic media surface finish and, in particular, to an improved system, method, and apparatus for measuring the true roughness of highly granular perpendicular media.
2. Description of the Related Art
Understanding and controlling the surface finish (i.e., “roughness”) of magnetic media is a significant parameter in the manufacture of hard disk drives. Roughness affects corrosion and the overall hard disk drive performance. Perpendicular media performance is particularly sensitive to roughness since these structures are highly granular and, thus, difficult to cover with overcoats.
It has been demonstrated that atomic force microscopy (AFM) may be used to measure roughness. AFM is particularly well suited to measure the highest elevations or “peaks” (i.e., Rp) of perpendicular media at an order of magnitude of about 10 nm at a lateral scale of about 1 μm. Again, such measurements are an important indicator of corrosion performance for production media.
As more exotic oxides are used as segregants in perpendicular media, it has been found that although Rp may remain the same, the depths of the lowest elevations, or the “valleys” between the peaks, are becoming more difficult to measure. In addition, the widths or gaps between the valleys also are becoming narrower (i.e., orders of magnitude smaller; e.g., nm instead of μm) such that measurement tools are unable to probe such topography.
Thus, there are no reliable means to obtain this information since the valley gaps are much narrower than the tips of the AFM instruments, which have a minimum radius that is much larger than the size of the features being measured. This problem is further exacerbated as the grain size continues to be reduced as novel oxides are employed. For example, most AFM measurements are simply truncated when they are physically unable to perform precise measurements. As a result, the corrosion-related failures of some novel media cannot be predicted. Thus, an improved solution for measuring the true roughness of highly granular perpendicular media would be desirable.